What's happens in D3 baseball during Fall?

Regarding the school you are dealing with... I recall in the past being quite surprised at how late they get started.  If still the same, nothing until well after school starts.  I'll check with a newer roster kid near me (I can part of his back yard from where I sit right now) to see if he has any more current intel.

I ran into a friend of mine the other day, who's son plays at a D3 college and thought I'd mention something (not the same topic, but I thought it was a good idea).  After his second year there, he decided to take summer school classes while he worked in the summer to lighten the fall / spring school load at the D3 (more time for baseball workouts and had more time on fewer classes = the grind of weight room at 6 AM, baseball, school, eat?, bed at 11 PM).  I believe he took the summer classes at a school near his home and could transfer the credits to the D3 after completion.

I think the biggest thing in all levels of college baseball coming in is this. Be prepared to compete from day one.  Do all the summer work of getting in excellent shape, lift, throw, hit, etc. What I saw at son's school last year is a lot of conditioning and right out of the gate. No easing into it.

Guys were competing day one for playing time. My son said he had never worked harder in his life that that fall. He spent his summer running, lifting and all the coaches workout routine and he said it was still crazy hard.

Not sure of your son's school but lots of D3 have way more guys come in fall than they need and basically only 10-11 position players and 7-8 pitchers get any real playing time in spring. Those jobs for the most part were won in the fall.

So my advise is simply be ready to compete day one. Be in the best baseball shape he can possibly be in 

From what I have seen every program has a different tempo and style, some start early and finish early. (East.Northern schools) Some start later and go later. Some are less intense than others.

My son's old program gave kids a couple of weeks to get settled in to school, then at 2 weeks they had a team meeting and laid out the fall. Lifting and individual skill work the first part of fall, then "captains" practices (run by upper classmen, no coaches) then about 6 weeks prior to their "fall world series" coach run practices, with live scrimmages. Fall world series right before Thanksgiving weekend and then they were back to individual work and weight room until January practice started when they returned from Christmas break. Fall World Series and late fall practices set pecking order for the season start.

As a rule Freshmen were not expected to contribute, but were always given a shot and there were always a couple that earned playing time, some significant.

There were always players out at the field during the day getting their work in, even prior to team meetings and freshmen were usually shown around by upper classmen. 

At first I thought it was odd for the slow start, but it really is a long grind and the coaching staff knows this and gives new players time to adjust as well as many of the kids are coming back from summer ball, which is even a bigger grind for some players so they need some down time, prior to getting after it again. 

I guess it would make sense that the fall would start a little slow -- what with many of the returning players having played summer collegiate ball and the new guys needing to get their feet wet school wise and all.  Plus D3 is not D1 so even the most competitive D3 have to give student-athletes space to be students first, I would guess. (Still the consistent message from his coaches is that "everyday we work to win the college world series" )